The proposed research involves the use of nuclear magnetic resonance for the study of the solution structure of transfer RNA and tertiary structural changes resulting from metal ion and oligonucleotide binding. A second major area is the use of nuclear magnetic relaxation techniques for studies of the catalytic and allosteric mechanisms of aspartate transcarbamylase from E. coli. Conformational changes of tRNAtyr and tRNAval from E. coli will be monitored by observing changes in the high resolution proton spectrum of modified base resonances in order to determine the effect of oligonucleotide and metal ion binding on tertiary structure. These changes are of importance in the mechanism of protein synthesis. Nuclear relaxation times of substrates and nucleotides are affected by their exchange from sites on aspartate transcarbamylase. These effects can be interpreted in terms of rates of dissociation, changes in stoichiometry and immobilization of bound molecules. The mechanism of catalysis and the effect of nucleotides on the binding of substrates are being explored in this manner.